High-power, high-brightness continuous wave (CW) and mode-locked lasers remain of interest to the research community. The use of semiconductor lasers for this purpose provides well-recognized advantages, not the least of which are cost efficiency and ease of handling, in practice. A conventional approach to achieving high laser power outputs from the semiconductor lasers is to utilize a so-called resonant periodic gain (RPG) structure, which includes a multiplicity of sequentially-disposed quantum wells (QWs) limited on one side by a distributed Bragg grating (DBR) reflector and, on the other side, an optical window through which laser emission is delivered outside of the cavity. The optical window sometimes includes anti-reflectance and/or high-reflectance (AR/HR) or other thin-film optical coatings, terminating the cavity at the interface with the ambient medium (such as air). A schematic diagram illustrating such structure is shown in FIG. 1.
While some of the highest power outputs have been demonstrated with the use of such structures (for example, outputs greater than 100 Watts of total power; or 15 Watts for a single-mode narrow-linewidth power output; or about 5 Watts of output via 680-femtosecond duration pulses), practice and related art clearly demonstrate that the RPG-structure-based lasers prove to be quite inefficient in achieving short-pulsed laser operation—for example, in generation of a train of pulses with durations below 100 fs—let alone in generation of sub-100 fs pulses at high average power. While some attempts to reach the pulsed operation (with 100 fs pulses) have been made, the problem of unreliable stability of such operation, caused by depletion of excited carriers at substantially single optical frequency, has not been resolved.
Given that operationally-stable sub-100 fs pulsed lasing with high gain (at high power levels) remains of interest in a multitude of applications (including medicine, biology, sampling/probing of ultrafast processes, and fast optical data communications, to name just a few), there remains a need in a semiconductor laser configuration that differs from the conventional RPG configuration to overcome the existing problems.